Arsenal lost ground in the race to secure a top-four finish as the Gunners slumped to a surprise 3-2 defeat against Swansea City, while Mark Hughes' debut as QPR boss ended in a 1-0 loss at Newcastle United on Sunday.
Arsene Wenger's side needed a win at the Liberty Stadium to keep pace with fourth-placed Chelsea, but Danny Graham's second-half winner condemned the north Londoners to their second successive league defeat.
Fifth-placed Arsenal, beaten by Fulham in their last league outing, are now four points behind Chelsea and 10 behind Tottenham in third.
Wenger left Thierry Henry on the bench despite his match-winning cameo role against Leeds United at the start of his brief return on loan from New York Red Bulls.
It did not look like Henry would be missed as Robin van Persie put Arsenal in front in the fifth minute.
After a magnificent 2011, this was van Persie's first goal of the new year and the Dutch forward took it in style, running onto Andrey Arshavin's pass before clipping a cool strike past Swansea goalkeeper Michel Vorm at his near post.
But Swansea have lost only once at home since winning promotion from the Championship and the Welsh club drew level in the 16th minute when Scott Sinclair converted a penalty after Aaron Ramsey was harshly ruled to have tripped Nathan Dyer.
Swansea took the lead in the 57th minute when Ramsey allowed Joe Allen to steal possession and slip a pass to Dyer, who punished Arsenal's poor marking with a ferocious strike past Wojciech Szczesny.
Henry made his return to the Premier League after a five-year absence in the the 63rd minute and the Gunners drew level thanks to Theo Walcott's composed finish six minutes later.
However, Arsenal's defensive frailties were exposed less than 60 seconds later as Swansea striker Graham found space to drill a superb shot into the far corner of Szczesny's goal and secure the hosts' first win over their visitors since 1982.
In the day's early game, new QPR boss Hughes saw Leon Best give Newcastle victory at St James' Park.
Hughes was appointed on Tuesday following Neil Warnock's sacking, but the arrival of the former Fulham, Manchester City, Blackburn Rovers and Wales boss failed to galvanise his new team, who remain third-bottom of the table.
Best is deputising for Demba Ba, currently away on Africa Cup of Nations duty with Senegal, and he ensured the in-form striker would not be missed with a fine winner in the 37th minute to lift Newcastle into sixth place - four points off the Champions League spots.
"I was pleased with the players' application - they gave me everything they had," said Hughes.
"Obviously we've been done with a little bit of individual skill in our own box. We created a number of reasonable chances and on another day those will go in for us.
"It would have been ideal obviously if we could have got something out of the game because overall I felt we deserved something.
"It's a hard place to come, we understand that. It was never going to be easy so that's why I'm encouraged by what I saw."
Hughes - who made six changes to QPR's starting line-up - must have been encouraged when Shaun Wright-Phillips and Jay Bothroyd hit the woodwork early on, while Newcastle lost influential midfielder Yohan Cabaye to injury in the 25th minute.
But Alan Pardew's team took the points thanks to a clinical effort from Best, who cleverly tricked his way past Luke Young before slotting home his first goal since September.